Heat exchanger having a contoured insert and method of assembling the same

ABSTRACT

The present invention provides a heat exchanger for transferring heat between a first working fluid and a second working fluid, including a pair of spaced apart headers, a number of tubes extending between the pair of headers and providing a flow path for the first working fluid and being positioned along a flow path for the second working fluid, and an insert supportable in one of the tubes and having a fold extending in a direction substantially parallel to the flow path for the first working fluid through the tubes. The fold can define first and second legs of the insert. A dimple can be formed on the first leg and a protrusion can be formed on the second leg opposite to the dimple on the first leg.

FIELD OF THE INVENTION

The present invention relates to heat exchangers and more particularly,to an exhaust gas recirculation cooler and a method of assembling thesame.

SUMMARY

In some embodiments, the present invention provides a heat exchanger fortransferring heat between a first working fluid and a second workingfluid. The heat exchanger can include a pair of spaced apart headers, anumber of tubes extending between the pair of headers and providing aflow path for the first working fluid and being positioned along a flowpath for the second working fluid, and an insert supportable in one ofthe tubes and having a fold extending in a direction substantiallyparallel to a length of the one of the tubes between the pair ofheaders. The insert can include a number of dimples extending into andspaced along the fold.

The present invention also provides a heat exchanger for transferringheat between a first working fluid and a second working fluid includinga pair of spaced apart headers, a number of tubes extending between thepair of headers and providing a flow path for the first working fluidand being positioned along a flow path for the second working fluid, andan insert supportable in one of the tubes and having a fold extending ina direction substantially parallel to the flow path for the firstworking fluid through the tubes. The fold can define first and secondlegs of the insert. A dimple can be formed on the first leg and aprotrusion can be formed on the second leg opposite to the dimple on thefirst leg.

In some embodiments, the present invention provides a heat exchanger fortransferring heat between a first working fluid and a second workingfluid including a pair of spaced apart headers, a number of tubesextending between the pair of headers and providing a flow path for thefirst working fluid and being positioned along a flow path for thesecond working fluid, and an insert supportable in one of the tubes andhaving a serpentine fold extending in a direction substantially parallelto a length of the tube between the pair of headers.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bottom perspective view of a heat exchanger according tosome embodiments of the present invention.

FIG. 2 is a partially cut-away view of a portion of the heat exchangershown in FIG. 1.

FIG. 3 is an exploded perspective view of a portion of a tube and aninsert of the heat exchanger shown in FIG. 1.

FIG. 4 is a perspective view of a portion of the insert shown in FIG. 3.

FIG. 5 is an exploded perspective view of a portion of a tube and aninsert according to an alternate embodiment of the present invention.

FIG. 6 is a perspective view of a portion of the insert shown in FIG. 5.

FIG. 7 is a top view of a partially formed insert that can bemanufactured according to the method shown in FIG. 9.

FIG. 8 is a perspective view of a partially formed insert that can bemanufactured according to the method shown in FIG. 10.

FIG. 9 illustrates a method for forming the insert shown in FIG. 5.

FIG. 10 illustrates another method for forming the insert shown in FIG.5.

FIG. 11 is a perspective view of a section of the insert forming deviceshown in FIG. 10.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items.

Unless specified or limited otherwise, the terms “mounted,” “connected,”“supported,” and “coupled” and variations thereof are used broadly andencompass both direct and indirect mountings, connections, supports, andcouplings. Further, “connected” and “coupled” are not restricted tophysical or mechanical connections or couplings.

Also, it is to be understood that phraseology and terminology usedherein with reference to device or element orientation (such as, forexample, terms like “central,” “upper,” “lower,” “front,” “rear,” andthe like) are only used to simplify description of the presentinvention, and do not alone indicate or imply that the device or elementreferred to must have a particular orientation. In addition, terms suchas “first” and “second” are used herein for purposes of description andare not intended to indicate or imply relative importance orsignificance.

FIGS. 1-4 illustrate a heat exchanger 10 according to some embodimentsof the present invention. In some embodiments, including the illustratedembodiments of FIGS. 1-4, the heat exchanger 10 can operate as anexhaust gas recirculation cooler (EGRC) and can be operated with theexhaust system of a vehicle. In other embodiments, the heat exchanger 10can be used in other (e.g., non-vehicular) applications, such as, forexample, in electronics cooling, industrial equipment, building heatingand air-conditioning, and the like. In addition, it should beappreciated that the heat exchanger 10 of the present invention can takemany forms, utilize a wide range of materials, and can be incorporatedinto various other systems.

During operation and as explained in greater detail below, the heatexchanger 10 can transfer heat from a high temperature first workingfluid (e.g., exhaust gas, water, engine coolant, CO₂, an organicrefrigerant, R12, R245fa, air, and the like) to a lower temperaturesecond working fluid (e.g., water, engine coolant, CO₂, an organicrefrigerant, R12, R245fa, air, and the like). In addition, whilereference is made herein to transferring heat between two workingfluids, in some embodiments of the present invention, the heat exchanger10 can operate to transfer heat between three or more fluids.Alternatively or in addition, the heat exchanger 10 can operate as arecuperator and can transfer heat from a high temperature location of aheating circuit to a low temperature location of the same heatingcircuit. In some such embodiments, the heat exchanger 10 can transferheat from a working fluid traveling through a first portion of the heattransfer circuit to the same working fluid traveling through a secondportion of the heat transfer circuit.

As shown in FIGS. 1 and 2, the heat exchanger 10 can include a firstheader 18 and a second header 20 positioned at respective first andsecond ends 22, 24 of a stack of heat exchanger tubes 26 having outersurfaces 28 (shown in FIGS. 1, 3, and 5). In the illustrated embodimentof FIGS. 1-4, the first end 22 is secured to a first collecting tank 30and the second end 24 is secured to a second collecting tank 32. Inother embodiments, the heat exchanger 10 can include a single header 18and/or a single tank 30 located at one of the first and second ends 22,24 or at another location on the heat exchanger 10.

As shown in FIGS. 1 and 2, each of the tubes 26 can be secured to thefirst and second headers 18, 20 such that a first working fluid flowingthrough the heat exchanger 10 is maintained separate from a secondworking fluid flowing through the heat exchanger 10. More specifically,the heat exchanger 10 defines a first flow path (represented by arrows34 in FIG. 1) for the first working fluid and a second flow path(represented by arrows 36 in FIG. 1) for a second working fluid, and thefirst and second flow paths 34, 36 are separated such that the firstworking fluid is prevented from entering the second flow path 36 andsuch that the second working fluid is prevented from entering the firstflow path 34.

In some embodiments, such as the illustrated embodiment, the tubes 26are secured to the first and second headers 18, 20 and the first andsecond tanks 30, 32 such that the first working fluid enters the heatexchanger 10 through a first inlet aperture 40 in the first tank 30,travels through the tubes 26 of the heat exchanger 10 along the firstflow path 34, and is prevented from entering the second flow path 36. Inthese embodiments, the tubes 26 can be secured to the first and secondheaders 18, 20 and the first and second tanks 30, 32 such that thesecond working fluid enters the heat exchanger 10 through a second inletaperture 42 in the second tank 32, travels through the heat exchanger 10along the second flow path 36 between the tubes 26, and is preventedfrom entering the first flow path 34.

In other embodiments, the tubes 26 can have other orientations andconfigurations and the first and second flow paths 34, 36 can bemaintained separate by dividers, inserts, partitions, and the like. Instill other embodiments, the first flow path 34 can extend through someof the tubes 26 while the second flow path 36 can extend through othertubes 26.

As shown in FIG. 2, the headers 18, 20 can have apertures sized toreceive one or more of the tubes 26. As illustrated by FIGS. 1 and 2,the first working fluid flowing along the first flow path 34 can enterthe tubes 26 through apertures formed in the first header 18. In theseembodiments, the first header 18 can also direct the second workingfluid from the second inlet aperture 42 between adjacent tubes 26 andcan prevent the second working fluid from flowing into the tubes 26. Thefirst header 18 can also prevent the first working fluid from flowingbetween the tubes 26.

In the illustrated embodiment, the heat exchanger 10 is configured as across-flow heat exchanger such that the first flow path 34 or a portionof the first flow path 34 is opposite to the second flow path 36 or aportion of the second flow path 36. In other embodiments, the heatexchanger 10 can have other configurations and arrangements, such as,for example, a parallel-flow or a counter-flow configuration.

In the illustrated embodiment, the heat exchanger 10 is configured as asingle-pass heat exchanger with the first working fluid traveling alongthe first flow path 34 through at least one of a number of tubes 26 andwith the second working fluid traveling along the second flow path 36between adjacent tubes 26. In other embodiments, the heat exchanger 10can be configured as a multi-pass heat exchanger with the first workingfluid traveling in a first pass through one or more of the tubes 26 andthen traveling in a second pass through one or more different tubes 26in a direction opposite to the flow direction of the first working fluidin the first pass. In these embodiments, the second working fluid cantravel along the second flow path 36 between adjacent tubes 26.

In yet other embodiments, the heat exchanger 10 can be configured as amulti-pass heat exchanger with the second working fluid traveling in afirst pass between a first pair of adjacent tubes 26 and then travelingin a second pass between another pair of adjacent tubes 26 in adirection opposite to the flow direction of the second working fluid inthe first pass. In these embodiments, the first working fluid can travelalong the first flow path 34 through at least one of the tubes 26.

In the illustrated embodiment, the heat exchanger 10 includes seventubes 26, each of which has a substantially rectangular cross-sectionalshape. In other embodiments, the heat exchanger 10 can include one, two,three, four, five, six, eight, or more tubes 26, each of which can havea triangular, circular, square or other polygonal, oval, or irregularcross-sectional shape.

As mentioned above, in some embodiments, the second flow path 36 or aportion of the second flow path 36 can extend across the outer surface28 of one or more of the tubes 26. In some such embodiments, ribs 56(see FIG. 3) can be formed along the outer surfaces 28 of the tubes 26to at least partially define channels 58 between adjacent tubes 26.Alternatively, as shown in FIG. 5, the tubes 26 of the heat exchanger 10can be generally oval shaped (i.e., a simple extruded tube) and devoidof ribs 56 defining channels 58. A housing can be provided around thetubes 26 to prevent the second fluid from leaking out of the heatexchanger 10 between adjacent tubes 26. In such an embodiment, thehousing would define the second flow path 36 between/around the tubes26.

In embodiments, such as the illustrated embodiment of FIGS. 1-4, havingoutwardly extending ribs 56, the ribs 56 of each tube 26 can be securedto an adjacent tube 26. In some such embodiments, the ribs 56 of onetube 26 can be soldered, brazed, or welded to an adjacent tube 26. Inother embodiments, adjacent tubes 26 can be secured together withinter-engaging fasteners, other conventional fasteners, adhesive orcohesive bonding material, by an interference fit, etc. In addition, ahousing can be provided around the tubes 26 of the embodimentillustrated in FIGS. 1-4.

Additional elevations, recesses, or deformations 64 can also oralternatively be provided on the outer surfaces 28 of the tubes 26 toprovide structural support to the heat exchanger 10, prevent thedeformation or crushing of one or more tubes 26, maintain a desiredspacing between adjacent tubes 26, improve heat exchange between thefirst and second working fluids, and/or generate turbulence along one orboth of the first and second flow paths 34, 36.

The heat exchanger 10 can include inserts 66, which improve heattransfer between the first and second working fluids as the first andsecond working fluids travel along the first and second flow paths 34,36, respectively. The inserts 66 can provide the heat exchanger core(i.e., the tubes 26) with increased surface area for distribution of theheat provided by the first and/or second working fluids. As shown inFIGS. 2, 3, and 5, the inserts 66 can be positioned in the tubes 26.Alternatively or in addition, inserts 66 can be positioned betweenadjacent tubes 26. In other embodiments, inserts 66 can be integrallyformed with the tubes 26 and can extend outwardly from the outersurfaces 28 of the tubes 26, or alternatively, inwardly from innersurfaces of the tubes 26. In some embodiments, the inserts 66 canimprove the durability and strength of the heat exchanger 10. Theconfigurations (geometrical and topographical) of the inserts 66 can besuch that the expansion and contraction experienced by the material dueto thermal fluctuations can be compensated for with increasedflexibility (discussed in further detail below).

In the illustrated embodiment of FIG. 2, an insert 66 is supported ineach of the tubes 26, and extends along the entire length orsubstantially the entire length of each of the tubes 26 between oppositeends 68 of the tubes 26. As FIG. 2 illustrates, the insert 66 can alsoor alternatively extend across the entire width or substantially theentire width of each of the tubes 26 between opposite sides of the tubes26. In other embodiments, an insert 26 can be supported in only one orless than all of the tubes 26, and the insert(s) 66 can extendsubstantially the entire length of the tube(s) 26 between opposite ends68 of the tube(s) 26, or alternatively, the insert 66 can extend throughthe tube(s) 26 along substantially less than the entire length of thetube(s) 26. In still other embodiments, two or more inserts 66 can besupported by or in each tube 26. In some embodiments, the inserts 66 canbe secured to the tubes 26. In some such embodiments, the inserts 66 aresoldered, brazed, or welded to the tubes 26. In other embodiments, theinserts 26 can be connected to the tubes 26 in another manner, such as,for example, by an interference fit, adhesive or cohesive bondingmaterial, fasteners, etc.

In some embodiments, the ends 68 of the tubes 26 can be press-fit intoone or both of the first and second headers 18, 20. In some suchembodiments, the ends 68 of the tubes 26 and the inserts 66 supported inthe tubes 26 or between the tubes 26 can be at least partially deformedwhen the tubes 26 and/or the inserts 66 are press-fit into the firstand/or second headers 18, 20. As such, the tubes 26 and/or the inserts66 are pinched and maintained in compression to secure the tubes 26and/or the inserts 66 in a desired orientation and to prevent leaking.In some embodiments, the tubes 26 can be brazed, soldered, or welded tothe first and/or second headers 18, 20.

In the illustrated embodiments, roll-formed sheets of metal are foldedto form the inserts 66 in a method that will be described in furtherdetail below. In other embodiments, the inserts 66 can be cast or moldedin a desired shape and can be formed from other materials (e.g.,aluminum, copper, iron, and other metals, composite material, alloys,and the like). In still other embodiments, the inserts 66 can be cut ormachined to shape in any manner, can be extruded or pressed, can bemanufactured in any combination of such operations, and the like.

As most clearly shown in FIGS. 3 and 7, the insert 66 can be corrugatedand have an overall length L, width W, and height H. The length L of theinsert 66 is defined as the general direction of fluid flow within thetube 26 (i.e., from the first header 18 to the second header 20). Asshown in the embodiment illustrated in FIG. 3, each fold forms aserpentine spine 76 that extends generally in parallel to the length Lof the insert 66.

The illustrated embodiment of the insert 66 includes a series ofparallel-running spines 76 that form alternating peaks 78 and valleys 80along the width W of the insert 66. As shown in FIG. 2, the peaks 78 andvalleys 80 can engage respective upper and lower interior sides (e.g.,between upper and lower sides in FIGS. 2, 3, and 5) of a tube 26. In theillustrated embodiment, legs or flanks 82 extend between each pair ofadjacent folds (i.e., from a peak 78 to a valley 80 or vice versa) alongthe length L, to give the insert 66 a height H. In addition, the inserts66 of some embodiments can have pointed, squared, or irregularly shapedpeaks 78 and/or valleys 80. The resulting lateral edge of the insert 66of the illustrated embodiment, as shown in FIGS. 2 and 3 can begenerally wavy. However, in other embodiments, the lateral edge can begenerally sinusoidal or saw-toothed, among other shapes. The structuralelements formed by each fold 76 of the corrugated insert 66 aredescribed more specifically with reference to FIGS. 4 and 6 below.

As illustrated by FIGS. 4 and 6, a first leg 82 a can be at leastpartially defined on one side of a spine 76 and a second leg 82 b can beat least partially defined on the other side of the spine 76. Fold 76 ais positioned immediately adjacent to the first leg 82 a and defines aheight h of the leg 82 a. Similarly, fold 76 b is positioned at thedistal end of the second leg 76 b, which has the same height h. Thespace S between adjacent legs 82 a, 82 b is defined as the distancebetween the points located at the same distance along length L andheight h of each leg 82. The legs 82 of the insert 66 can also havevarious topographical configurations. For example, at one point alongthe length L, the legs 82 can be contoured or wavy (i.e., when viewedfrom an end of the insert 66 as shown in FIGS. 3 and 4, and at anotherpoint along the length L, the legs 82 can be straight.

As shown in FIGS. 3-8, the legs 82 can include contour elements such asdimples 86 and protrusions 88 spaced along their length L. Theseelements are deformations in the material that forms the insert 66 anddo not pierce or provide connections between opposite sides of theinsert 66. In some such embodiments, a dimple 86 formed on one side of aleg 82 can consequently form a protrusion 88 on the opposite side of theleg 82 (i.e., a dimple 86 is a geometric complement of protrusion 88).The contour elements formed in the insert 66 can appear as pyramid,frustum, prism, and/or hemispheroid-like projections or dimples, amongothers. In the illustrated embodiment, the contour elements each havetwo planes of symmetry (one of which is the length L, space s plane, andthe other of which is the height h, space s plane). As such, the upperhalf of the contour element is a mirror image of the bottom half (withrespect to the height h of the leg 82 it is positioned on). Similarly,the left half of the contour element is a mirror image of the right half(with respect to the length L of the leg 82 it is positioned on). Insome embodiments, a protrusion 86 in one leg 82 can be positioned suchthat it is at least partially receivable in a dimple 88 in an adjacentto leg 82 (i.e., at the same distance along height h and length L ofeach leg ).

In some embodiments, contour elements can extend along the entire heighth of the leg 82 from one fold 76 to an adjacent fold 76 (i.e., from apeak 78 to an adjacent valley 80 or vice versa). Each contour elementhas a width d, as shown in FIG. 6. In the illustrated embodiment, thewidth d also indicates the spacing between similar contour elements. Inother embodiments, the spacing between similar contour elements can begreater than the width d of an intervening or alternating contourelement.

As shown in FIG. 4, the serpentine shape of the spine 76 is determinedby the geometry and placement of the dimples 86 and protrusions 88. Inthe illustrated embodiments, dimples 86 are alternated with protrusions88 along the length L of each leg 82, and each of the contours extendsbetween adjacent folds 76. Accordingly, a number of dimples 86 and anumber of protrusions 88 can be spaced along the edge of each fold 76.FIG. 4 includes reference measurements to more clearly illustrate thegeometry of the insert 66. Specifically, reference a indicates thedistance between the midline of the fold 76 and the edge of a dimple 86,reference b indicates the distance between the midline of the fold 76and the edge of a protrusion 88, and reference c indicates the lateraldistance (i.e., the direction normal to the length L of the insert andwidth d of the contour element) from the edge of the contour element atthe fold 76, to its outermost point/extension.

As illustrated in FIGS. 3-6, an insert 66 formed with longitudinal rowsof alternating contour elements 86, 88, can be folded such that thespace S between adjacent legs 82 at a particular height h can begenerally constant along their length L. Thus, the flow pathcross-sectional area is essentially constant along the length L betweenopposite ends 68 of the tube 26. Accordingly, the first flow path 34 ismade circuitous and is consequently longer than a straighter flow path.Such an insert configuration can increase turbulence of the workingfluid and consequently allow for more efficient heat transfer withoutcausing significant pressure changes/buildup along the length L of theinsert 66. Additionally, contour elements formed in the inserts 66 canimpact the shape of the spine 76. For example, FIGS. 3-8 show how apattern of dimples 86 and protrusions 88- specifically longitudinal rowsof the continuously alternating contour elements—can create aserpentine-shaped spine 76. As such, even the flow path immediatelyadjacent to the inner surfaces of the tube 26 is elongated and madecircuitous. The serpentine shape of the spine 76 can also provide areinforced connection between the tube 26 and the insert 66 which canalso improve heat transfer.

In embodiments having inserts 66 with wavy or contoured cross-sections,such as the illustrated embodiments, the inserts 66 operate as elasticmembers to absorb or at least partially absorb vibrations and/or toabsorb expansions and contractions of the inserts 66 caused byfluctuating temperatures of the first and/or second working fluids. Insome such embodiments, the elasticity of the contoured inserts 66prevents or reduces cracking and breaking of the inserts 66.Alternatively or in addition, the elasticity of the contoured inserts 66prevents and/or reduces cracking and breaking of connections (e.g.,solder points, braze points, weld points, etc.) between the spines 76 ofthe inserts 66 and the interior sides of the tubes 26.

As shown in FIGS. 5-8, in some embodiments, contours 86, 88 can extendcontinuously from a first lateral edge 92 to a second lateral edge 94,along the length L of a leg 82. In other embodiments, such as thoseillustrated in FIGS. 2-4, contours only extend continuously along thelength L of a middle portion of the insert 66, while the edges 92, 94have a different topographical configuration, such as, for example,wavy. The contoured portion can allow for changes in length L (i.e.,longitudinal flexibility), while the wavy edges can compensate forchanges in height h of the legs 82 (i.e., vertical flexibility). Thiscan be desirable in embodiments where the height of the insert H isconstrained by connection to the inner surfaces of the tube 26,especially where the tube ends 68 are further constrained by the firstand second headers 18, 20.

FIG. 9 illustrates a method of forming an insert 66 for a heat exchanger10 according to some embodiments of the present invention. The methodinvolves roll-forming a pattern of dimples 86 and protrusions 88 into asheet of deformable heat conducting material 100 (e.g, aluminum, copper,bronze, and alloys including one or more of these metals). To clarifythe description, the process of contour formation is shown in FIG. 9(and discussed with reference to FIG. 9) as occurring in two distinctand consecutive steps for a particular longitudinally-located, lateralsection of the sheet. First, at the right-hand side of the figure,dimples 86 are roll-formed, then, to the left of that, protrusions 88are roll-formed. However, in practice, roll-formation of dimples 86 andprotrusions 88 can be executed simultaneously (as described andillustrated with respect to the alternative embodiments shown in FIGS.10 and 11 below). Whether the dimples 86 and protrusions 88 are formedconsecutively or simultaneously, the roll-formed insert 66 in FIG. 9then undergoes a folding process (right-hand side of the figure) tocreate spines 76. The steps discussed above can be incorporated into ahigh-speed assembly process which is described in more detail below.

As shown in FIG. 9, the method can make use of a firstcylindrically-shaped roller 102 having projections 104 positioned inlongitudinal rows along its curved exterior surface 106. The firstroller 102 can be rotated about its axis 108 as it makes contact with afirst side 110 of the sheet of deformable material 100, positionedtangentially with respect to the curved surface 106. The weight of thefirst roller 102 can be used to exert pressure on the deformablematerial such that the projections 104 form dimples 86 in the material100. In other embodiments, the sheet of material 100 can be forced intocontact with the roller 100 by other means to form dimples 86.

The shape and size of the projections 104 with respect to the thicknessof the sheet of material 100 can be such that the dimples 86 formed bycontact of projections 104 with the first side 110 of the sheet ofdeformable material 100 create their geometric complement on a secondside (not visible) of the sheet 100 which is opposite to the first side110. Thus, dimples 86 and protrusions 88 can be simultaneously formed onthe first side 110 and an opposite second side of the sheet 100,respectively.

A second cylindrically-shaped roller 112 having projections 114positioned in longitudinal rows along its curved surface 116 can bepositioned adjacent to the opposite side of the sheet 100 from the firstroller 102. The second roller 112 can also be rotated about its axis 118as it makes contact with the second side of the sheet of deformablematerial 100, positioned tangentially with respect to the curved surface116. In this way, dimples 86 can be formed on the second side of thesheet 100, and corresponding projections 88 can be formed on the firstside 110.

The rollers 102, 112 can be formed by axially stacking cylindricaldisks, the boundaries of which are illustrated by dashed lines in FIG.9. In some embodiments, disks with various shaped projections 114 and/orcircumferential spacing between projections 114 can be assembled into aroller that will form inserts 66 with different dimensions andgeographies. Similarly, the disks can be circumferentially staggered toprovide inserts 66 with more or less space between rows of contourelements, which can result in wider or narrower spines 76. The rollers102, 112 can be arranged with respect to each other such that thedimples 86 and protrusions 88 on each side of the sheet are formed atspecific locations with respect to each other. For example, FIGS. 7-9illustrate how the rollers 102, 112 can be aligned to form lateral andlongitudinal rows of alternating dimples 86 and protrusions 88 along thesheet 100. The lateral rows are separated by narrow gaps where the sheet100 can be folded to form corrugations such that the lateral rows becomelegs 82 and the gaps become spines 76. In the illustrated embodiment,the rollers 102, 112 are staggered slightly to form serpentine-shapedspines 76. In other embodiments, the rollers 102, 112 can be aligned toform straight spines 76. In still other embodiments, the positioning,size, and/or shape of the projections 104, 114 on the first and/orsecond rollers 102, 112 can be varied to change the geometry and/ortopography of the insert 66. In still other embodiments, curved surfaces106, 116 of the rollers 102, 112 can be provided with indentionscorresponding (i.e., in location, size, shape, etc.) to the projections114, 104 in the opposing roller 112, 102, in order to better define thecontours formed in the sheet 100.

FIG. 10 illustrates a method of forming inserts 66 according to anotherembodiment of the invention. The method illustrated in FIG. 10 usesstar-shaped rollers to simultaneously form contour elements andpartially fold the insert 66. A first star-shaped disk 120 represents afirst star-shaped roller that is positioned on a first side 110 of asheet of deformable material 100 in the illustrated embodiment of FIG.10. Along the circumference of the first disk 120, alternating ridges122 and crevasses 124 create the star shape of the disk. The ridges 122and crevasses 124 can contribute to the formation of peaks 78 andvalleys 80 as will be described in further detail below. Between eachridge 122 and crevasse 124 is formed a projection 126 or an indention128. The projections 126 and indentions 128 can form dimples 86 andprotrusions 88 in the insert as will also be discussed in further detailbelow. In some embodiments, such as the illustrated embodiment, theprojections 126 and indentions 128 can be geometric complements and havemultiple planes of symmetry as discussed previously with respect todimples 86 and protrusions 88. In other embodiments, the ridges 122 canbe geometric complements of crevasses 124.

A second star-shaped disk 130 in FIG. 10 represents a second star-shapedroller that can have alternating ridges 132 and crevasses 134 thatseparate alternating projections 136 and indentions 138 similar (i.e.,in shape, size, etc.) to those of the first disk 120. Alternatively orin addition, the projections 136 can be geometric complements ofindentions 128 and projections 126 can be geometric complements ofindentions 138, in which case, projections 126, 136 need not begeometric complements of indentions 128, 138 on the same disk. Thesecond star-shaped disk 130 is positioned on a second side 140 of thesheet of material 100.

The first and second star-shaped disks 120, 130 can be positioned withrespect to each other such that each ridge 122 of the first disk 120fits within a crevasse 134 of the second disk 130 and each ridge 132 ofthe second disk 130 fits within a crevasse 124 of the first disk 120 asthe disks 120, 130 turn on their respective axes. Thus, when the sheetof deformable material 100 is fed between the star-shaped disks 120,130, the corresponding ridges 122 and crevasses 134 fold the material toform peaks 78, and corresponding ridges 132 and crevasses 124 fold thematerial to form valleys 80. Similarly, the projections 126, 136 andcorresponding indentions 138, 128 form dimples 86 and protrusions 88 inthe insert 66.

Star-shaped rollers can be made up of star-shaped disks 120 that arestacked axially, similar to the arrangement discussed above with respectto the embodiment of FIG. 9. FIG. 11 illustrates how these star-shapeddisks 120 can be stacked in an alternating arrangement such that aprojection 126 in one disk is positioned adjacent an indention 128 in asecond disk. Adjacent disks can be staggered such that the ridges 122and crevasses 124 in one disk are not in direct alignment with theridges 122 and crevasses 124 in a second disk, as shown in FIG. 11. Bycomplementary positioning of two star-shaped rolls having thisarrangement of disks, an insert 66 can be formed having serpentinespines 76, as shown in FIGS. 3-8.

After the inserts 66 have been roll-formed and folded, they can be cutto the appropriate size and then inserted into tubes 26. In otherembodiments, the inserts 66 can be cut before they are folded.Alternatively, the tubes 26 can be assembled around the inserts 66. Instill other embodiments, the tubes 26 and the inserts 66 can be cut tosize simultaneously.

The embodiments described above and illustrated in the figures arepresented by way of example only and are not intended as a limitationupon the concepts and principles of the present invention. As such, itwill be appreciated by one having ordinary skill in the art that variouschanges in the elements and their configuration and arrangement arepossible without departing from the spirit and scope of the presentinvention.

1. A heat exchanger for transferring heat between a first working fluidand a second working fluid, the heat exchanger comprising: a pair ofspaced apart headers; a plurality of tubes extending between the pair ofheaders and providing a flow path for the first working fluid and beingpositioned along a flow path for the second working fluid; and an insertsupportable in one of the plurality of tubes and having a fold extendingin a direction substantially parallel to a length of the one of theplurality of tubes between the pair of headers, the insert including aplurality of dimples extending into and spaced along the fold.
 2. Theheat exchanger of claim 1, wherein the fold defines first and secondlegs of the insert, and wherein, at a height of the first leg betweenthe fold and a distal end of the first leg, a width between the firstand second legs is substantially constant between opposite ends of theinsert spaced apart in the direction of the fold.
 3. The heat exchangerof claim 1, wherein the fold defines first and second legs of theinsert, wherein the dimple extends across the first leg, and wherein thesecond leg includes an outwardly extending protrusion shaped to bematingly receivable in the dimple of the first leg.
 4. The heatexchanger of claim 1, wherein the fold is a first fold, wherein theinsert includes a second fold extending across the insert in a directionsubstantially parallel to the first fold, and wherein at least one ofthe plurality of dimples extends across a leg of the insert between thefirst fold and the second fold.
 5. The heat exchanger of claim 1,wherein the insert has as first side and a second side opposite to thefirst side, and wherein the plurality of dimples are formed on the firstside and form protrusions on the second side, the protrusions extendinginto the fold.
 6. The heat exchanger of claim 1, wherein the flow pathfor the first working fluid extends through the plurality of dimples toprovide a circuitous path between opposite ends of the tube.
 7. The heatexchanger of claim 1, wherein the plurality of dimples at leastpartially define an elastic region moveable relative to the tube in thedirection substantially parallel to the length of the tube toaccommodate thermal expansion of one of the tube and the insert.
 8. Theheat exchanger of claim 1, wherein the fold provides a non-linear spineof the insert.
 9. The heat exchanger of claim 1, wherein the heatexchanger is an exhaust gas recirculation cooler, and wherein the firstworking fluid is engine exhaust and the second working fluid is acoolant.
 10. The heat exchanger of claim 1, wherein the fold definesfirst and second legs of the insert, wherein the dimple extends acrossthe first leg at a distance from an inlet to the flow path for the firstworking fluid, and wherein a protrusion extends across the second legopposite to the dimple of the first leg.
 11. The heat exchanger of claim10, wherein a cross-sectional area of the flow path for the firstworking fluid is substantially the same between the first and secondlegs at the inlet to the flow path for the first working fluid andbetween the dimple and the protrusion.
 12. A heat exchanger fortransferring heat between a first working fluid and a second workingfluid, the heat exchanger comprising: a pair of spaced apart headers; aplurality of tubes extending between the pair of headers and providing aflow path for the first working fluid and being positioned along a flowpath for the second working fluid; and an insert supportable in one ofthe plurality of tubes and having a fold extending in a directionsubstantially parallel to the flow path for the first working fluidthrough the plurality of tubes, the fold defining first and second legsof the insert, a dimple being formed on the first leg and a protrusionbeing formed on the second leg opposite to the dimple on the first leg.13. The heat exchanger of claim 12, wherein a cross-sectional area ofthe flow path for the first working fluid is substantially the samebetween the first and second legs at an outlet of the flow path for thefirst working fluid and between the dimple and the protrusion.
 14. Theheat exchanger of claim 12, wherein the protrusion of the second leg isshaped to be matingly receivable in the dimple of the second leg. 15.The heat exchanger of claim 12, wherein the dimple extends into thefold.
 16. The heat exchanger of claim 12, wherein, at a height of thefirst leg between the fold and a distal end of the first leg, a widthbetween the first and second legs is substantially constant betweenopposite ends of the insert spaced apart in the direction of the fold.17. The heat exchanger of claim 12, wherein the fold is a first fold,wherein the insert includes a second fold extending across the insert inthe direction substantially parallel to the flow path for the firstworking fluid through the plurality of tubes, and wherein the dimpleextends across the first leg between the first fold and the second fold.18. The heat exchanger of claim 12, wherein the protrusion is a firstprotrusion, wherein the insert has a first side and a second sideopposite to the first side, and wherein the dimple extends across thefirst side and forms a second protrusion on the second side.
 19. Theheat exchanger of claim 12, wherein the fold provides a serpentine spineof the insert.
 20. The heat exchanger of claim 19, wherein the pluralityof dimples are roll-formed along the insert.
 21. The heat exchanger ofclaim 12, wherein the heat exchanger is an exhaust gas recirculationcooler, and wherein the first working fluid is engine exhaust and thesecond working fluid is a coolant.
 22. A heat exchanger for transferringheat between a first working fluid and a second working fluid, the heatexchanger comprising: a pair of spaced apart headers; a plurality oftubes extending between the pair of headers and providing a flow pathfor the first working fluid and being positioned along a flow path forthe second working fluid; and an insert supportable in one of theplurality of tubes and having a serpentine fold extending in a directionsubstantially parallel to a length of the tube between the pair ofheaders.
 23. The heat exchanger of claim 22, wherein the fold definesfirst and second legs of the insert, and wherein, at a height of thefirst leg between the fold and a distal end of the first leg, a widthbetween the first and second legs is substantially constant betweenopposite ends of the insert spaced apart in the direction of the fold.24. The heat exchanger of claim 22, wherein the fold defines first andsecond legs of the insert, wherein a dimple extends across the firstleg, and wherein the second leg includes an outwardly extendingprotrusion shaped to be matingly receivable in the dimple of the firstleg.
 25. The heat exchanger of claim 22, wherein the fold is a firstfold, wherein the insert includes a second fold extending across theinsert in a direction substantially parallel to the first fold, andfurther comprising a dimple extending across the insert between thefirst fold and the second fold.
 26. The heat exchanger of claim 22,wherein the insert has a first side and a second side opposite to thefirst side, and wherein a dimple is formed on the first side and forms aprotrusion on the second side, the protrusion extending into the fold.27. The heat exchanger of claim 22, further comprising a plurality ofdimples roll-formed along the insert.
 28. The heat exchanger of claim22, wherein a plurality of dimples are spaced along the fold.
 29. Theheat exchanger of claim 22 wherein the heat exchanger is an exhaust gasrecirculation cooler, and wherein the first working fluid is engineexhaust and the second working fluid is a coolant.
 30. The heatexchanger of claim 22, wherein the fold defines first and second legs ofthe insert, wherein a dimple extends across the first leg at a distancefrom an inlet to the flow path for the first working fluid, and whereina protrusion extends across the second leg opposite to the dimple of thefirst leg.
 31. The heat exchanger of claim 30, wherein a cross-sectionalarea of the flow path for the first working fluid is substantially thesame between the first and second legs at the inlet to the flow path forthe first working fluid and between the dimple and the protrusion.